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All countries take fire safety very seriously. In China, wood buildings must meet the same fire codes and standards and safety performance levels which apply to other forms of construction. In fact, when new systems, such as wood frame, or glulam construction are first introduced into a country like China, fire safety codes tend to be overly cautious because of the lack of domestic experience with the building system. Building regulations in Europe and North America have been based on function, rather than material, for many years. They stipulate what fire load the structural assemblies and members must be able to withstand and then require the designer to demonstrate that the stipulations can be met. Extensive research into the fire performance of structural wood assemblies and materials used in wood frame construction is now well underway in China. The Tianjin Fire Research Institute is working closely with fire safety research specialists from Europe, Canada, and the United States. They are assessing fire safety relating to new opportunities for wood construction in China and ensuring fire safety codes are up to date with the latest research (see Chapter 7, Codes and standards).International fire safety statistics show no difference in losses between countries which use wood extensively in construction and those which do not. In North America and Europe, statistics show that people are just as safe in a code-compliant wood frame house as they are in a code-compliant house built of light frame steel, concrete, or masonry.The limits for fire safety performance of large structural wood members can be readily determined and incorporated into building design. As wood burns in a predictable and controlled manner, it is possible to estimate how much of the cross-section of a structural member will remain unaffected by fire after a specified period of burning. Dimensions can then be specified to ensure the unaffected part of the cross section has the ability to bear the required load over the specified period. Steel, on the other hand, loses all its load-bearing capacity at the temperatures of a fully developed fire.The controlled charring rate of wood is clearly demonstrated when fire testing for structural glue laminated timber. The charring rate is 0.7mm/min, and the remaining unaffected wood and its load bearing capacity can be easily calculated as a function of time exposed to fire.
In fact, fire safety performance in conventional wood frame construction has little to do with the combustibility of the structural materials. It relates to the finished building assemblies, like walls and roofs, which are actually assessed in the tests. Wood framed assemblies are finished on the interior with gypsum wall board panels. These have very low combustibility ratings. Cavities are filled with non-combustible, mineral fibre insulation. Testing requires these assemblies to be burned under controlled conditions in fire research laboratories at very high temperatures until they fail structurally. Wood framed structural wall and roof assemblies are required to survive these high temperatures for a minimum of one hour before structural failure.Moreover, fire safety in low and medium density housing of all types is rarely related to structural failure, but rather to the inhalation of toxic smoke and gas. Fewer than 0.25 per cent of fire fatalities in these buildings are caused by the collapse of roofs, walls, or floors. Non-flammable surface materials, sprinkler systems and smoke detectors can be used to ensure safety from toxic gases during the early stages of a fire. Codes require that all buildings, including wood, be designed and constructed to provide residents with a fast and easy exit in the event of fire.
In human history, wood has always been an important building material.There are many examples of wooden buildings from around the world,including China, that have lasted for centuries in all climates. They provide evidence that wood construction can last virtually forever,providing it is designed and built properly to meet specific climatic conditions, and maintained appropriately over its full life cycle. Appropriate design, material selection, construction, and maintenance will ensure that wood is safe from the decay and mould associated with exposure to excessive moisture, as well as from the termite infestations found in the southern China regions.Durability depends on protecting wood from excessive moisture.Building envelopes should be designed to prevent water vapour condensation within envelope cavities and to allow any dampness to dry out. In wet climates, more steeply sloped roofs, large overhangs and rain screens can be used. As with any building system, the building envelope must be sealed against rain penetration around windows,doors, and other exterior wall openings, including roof penetrations and balconies.In areas with termite hazard, effective prevention and control can be achieved with appropriate design and construction practices. In recent years, multiple lines of defense have been developed and integrated into modern wood construction to ensure moisture and termite resistance. Exterior wood products used for decks and other landscaping projects are either made from naturally durable wood species, such as the heartwood of China fir, Western red cedar and yellow cedar, or pressure treated with chemical preservatives. Strict environmental and health regulations ensure these chemicals are benign to humans but resistant to insects and fungi.Good design, workmanship, and maintenance are also critical for prolonging the service life of outdoor wood products.Modern systems of wood frame construction also have a good record of durability. This building type has a long history in Europe and North America, and there are still houses standing from the original developments. Many North American and European wood houses are over a hundred years old. In 2005, 17 per cent of the US housing stock was over 75 years old.Wood frame is the most popular type of residential construction in North America, even for areas like Hawaii and the Southern USA, where decay and insect hazard are severe. Similar construction methods have also been adopted in areas such as New Zealand, the UK, Japan, Korea and China. Progress in design, material use and treatment, construction techniques and maintenance have been made in recent decades to make sure that wood buildings can endure indefinitely.Buildings are rarely demolished because they are beyond repair, or have become structurally unsound. Generally it is to make way for a larger or more modern building. Simple to maintain and repair, wood buildings are easily renovated to adapt to new requirements. At the end of their economic service life, they can be demolished, with recovered materials being reused, recycled or used as biomass energy.Forintek carried out a durability survey of wood frame houses in China during 2006 and 2007. Results demonstrated that, with the durability measures introduced into the relevant codes and standards in China,including the Shanghai Technical Specification for Wood-Frame Construction, wood construction in China is durable (See Chapter 7,Codes and standards).
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